UNIQUE GENE REGULATION GIVES CHILLY BUGS SURVIVAL ADVANTAGE
AT BOTTOM OF THE WORLD

COLUMBUS , Ohio  The larvae of Antarctic midges never
stop producing special proteins that minimize environmental stress,
allowing them to withstand a range of intense environmental conditions
in one of the world's harshest environments.

Scientists found that adult midges (Belgica antarctica)
lose their ability to continually express these protective heat-shock
proteins. Instead, like most animals, adult midges produce these
proteins only when they are stressed. The discovery currently
appears in the online edition of the Proceedings
of the National Academy of Sciences.

David
Denlinger

The proteins help defend the larval midges against environmental
stresses including temperature changes as well as changes in
water, oxygen and pH levels, said David
Denlinger, the study's lead author and a professor of entomology
at Ohio State University.

They've somehow figured out a way to maintain a level
of these heat-shock, or stress, proteins and still make proteins
that are vital for growth and development, he said.

This mechanism seems to offer the larvae protection during
their two-year life span, most of which is spent encased in ice.

All animals, including humans, make heat shock proteins, but
normally they only do so during times of extreme physical stress.
Curiously, adult midges don't express these proteins all the
time  only during periods of extreme environmental stress.
Yet when most insects express stress proteins, it temporarily
compromises the production of other proteins, Denlinger said.

The production of stress proteins usually brings development
to a halt, he said. But in this case, the larvae
merrily go about their business of feeding and growing while
producing their stress proteins.

The Antarctic midge is barely bigger than a grain of rice,
but it's still the largest free-roaming terrestrial animal to
inhabit Antarctica. The larvae resemble tiny black worms.

It's the largest species that has adapted to living
on the continent year-round, said Denlinger, adding that
other native animals, such as seals and penguins, spend much
of their time in the water. The midge is also the only insect
known to inhabit Antarctica.

He and his colleagues collected adult and larval midges during
field study tours to Antarctica in early 2005 and 2006. They
gathered insects from penguin colonies, where the midges feed
on algae and waste material.

The production of
stress proteins usually brings development to a halt, he
said. But in this case, the larvae merrily go about their
business of feeding and growing while producing their stress
proteins.

Penguins live along the Antarctic coast, where the average
summertime temperature is around 36°F (2°C). In laboratory
experiments, the researchers exposed the larvae and adults to
39.2°F (4°C) and to 68°F (20°C). They wanted
to see if the larval and adult midges showed any resilience against
the higher temperature.

Adult Antarctic midges usually live only a week or two in
the field and, in the laboratory, the adults lived for five to
six days at the lower temperature. But adult midges exposed to
the higher temperature died in less than a day.

However, the larval midges lived up to four days at the higher
temperature  four times longer than the adults.

The adults were considerably less heat-tolerant than
the larvae, Denlinger said. The larval midges continuously
express heat-shock proteins and are therefore prepared to respond
to the normal kinds of challenges that they face in the harsh
Antarctic environment. But the adults produce these proteins
only when directly confronted with an environmental challenge.

Clearly there is some kind of developmental switch that
happens between the larval stage and adulthood, he added.
We're just not sure what that is.

He said that the next step is to study larval midges during
the long Antarctic winter. While temperature may not play a large
role during this time, as the larvae are encased in ice for months,
many insects respond to seasonal changes in day length, which
regulate their development. Understanding what happens to larvae
during this time may give researchers more insight into the nature
and role of heat-shock proteins.